the usage of orakill??

i find the command orakill on my oracle8.1.6 nt version. and i want to know how to use it.
the usage tells me that orakill sid thread, and the thread can be obtained by the following command:
select spid,osuser,s.program from
v$process p,v$session s
where p.addr=s.paddr;
Though,this way does work,but i wonder,if i can use sqlplus to quest the thread,why don't i use: "alter system kill session" to kill that session, and to use that boring method?
can anyone tell me why?
and another question: when max process has been reached, what shall i do, how to identify those dead sessions and kill them in a quick way?
thanks.